#include <stdio.h>
#include <math.h>

int main() 
{
	double x1, y1;
	double x2, y2;
	double D;
	
	printf("input x1 y1: ");
	scanf("%lf %lf", &x1, &y1);
	printf("input x2 y2: ");
	scanf("%lf %lf", &x2, &y2);
	
	D = sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));
	
	printf("D:%lf", D);
	
	return 0;
}

